Fluid-operated control system



Aug. 28, 1945. w. w. SLOANE FLUID OPERATED CONTROL SYSTEM Filed Aug. 28, 1942 4 Sheets-Sheet 1 mA Mm Y W ?0 O M .l A 7 WM Q Aug. 28, 1945. w. w, SLOMQE 2,383,894

FLUID OPERATED CONTROL SYSTEM Filed Aug. 28, 1942 4 Sheets-Sheet 2 IN V EN TOR.

WWII/[Joana ATTORNEY Patented Aug. 28, 1945 FLUID-OPERATED CONTROL SYSTEM William W. Sloane, Chicago, Ill., assignor to Goodman Manufacturing Company, Chicago, 11]., a corporation of Illinois Application August 28, 1942, Serial No. 456,490

14 Claims.

This invention relates to a variable pressure fluid control valve mechanism adapted to supply pressures at values increasing or decreasing predetermined amount according to the position of the operating handl for the valve mechanism.

An object of my invention is to provide a novel form of control valve adapted to supply fluid under pressure to an hydraulically operated device, so arranged that as the control handle of the valve is turned to successive positions in one direction, the pressures of the fluid passing therefrom will increase in predetermined step by step values to a maximum, and as said valve is turned to successive positions in the opposite direction, the pressure of the fluid passing therefrom will decrease by predetermined values, and the pressures at any intermediate position between an on or off position will be substantially the same when the valve is being opened or closed.

Another object of my invention is to provide a variable pressur hydraulic control valve of the poppet type with means for reducing the unbalanced pressure on the valve seat by maintaining a pressure difference on opposite sides of the valve within predetermined limits, throughout its entire pressure range.

In carrying out my invention I provide a variable pressur hydraulic control valve including a piston type charging valve, a piston type discharge valve and poppet type pressure adjusting valves, and so connect and arrange these valves that the piston valves will maintain a pressure difference on opposite sides of the poppet valves within predetermined limits, throughout the en- 1 tire pressure rang thereof, when the control handle of the valve i turned in an on or an off direction.

Other objects and novel features of my invention will appear from time to time as the following speciflcation proceeds and with reference to the accompanying drawings wherein:

Figure 1 is a diagrammatic view illustrating an electrical control circuit for two motors of an electrical device such as a locomotive, and showing the fluid circuit for controlling operation thereof;

Figure 2 is a transverse sectional view taken through a controller constructed in accordance with my invention and showing a distributor valve connected thereto, for supplying fluid under pressure thereto;

Figure 3 is a top plan view of acasing for a reverse drum, with a fluid motor for operating the reverse drum shown in horizontal section;

Figure 4 is a fragmentary view in side elevation of the control casing, showing the valve for operating the reverse drum in transverse section;

Figure 5 i a view in side elevation of the control valve, for supplying fluid to the distributor valve under diflerent pressures, with parts of the v valve shown in section:

Figure 6 is a top plan view of the valveshown in Figure 5, with certain parts of the valve shown in horizontal section;

Figure '7 is a longitudinal sectional view taken through the valve shown in Figure 5;

Figure 8 is an enlarged detail partial fragmentary longitudinal sectional view of the valve shown in Figure '7, with the valve shown in a fully open position for the release of fluid to the discharge;

Figure 9 is an enlarged detail partial fragmentary longitudinal sectional view of the valve shown in Figure'i, in order to more clearly illustrate certain details thereof;

Figure 10 is a transverse sectional view taken substantially along line l0l0 of Figure 6;

Figure 11 is a transverse sectional view taken substantially along line llll of Figure 6; and

Figure 12 is a fragmentary detail view in side elevation of the valve shown in Figure 5, with certain parts shown in section, and illustrating more clearly certain details of the interlocking connection between the valve which controls reversal of the control circuit.

In Figure l of the drawings an electrical control circuit is shown which is particularly adapted to control the simultaneous operation of a plurality of motors, preferably the motors of a mine locomotive, and a hydraulic control system arranged in accordance with my invention, is shown for controlling operation of the electrical contacts of this control circuit. The motors are herein shown as being connected in parallel for simplicity, it being understood that the electrical control circuit may be so arranged as to connect them in series or in series parallel, or in any other desired manner. Said motors each consist of an armature l0 and a field H, and starting and stopping thereof is controlled by an electrical controller generally indicated by reference character l2. Said controller includes a. plurality of fluid-operated contactors l, 2, 3, 4, 5, 6, l and 8, for connecting the motors in the power line and for progressively cutting sections of a resistance l3 from the motor circuit.

The controller i2, as illustrated in Figure 2, includes a casing I4 forming an enclosure for the contactors l to 8 inclusive. Said contactors are each of the same construction so contactor I only will herein be shown and described in detail. Said contactor includes a stationary contact l5 mounted on an insulating board l6, and a movable contact I! engageable with said stationary contact. Said movable contact is mounted on a pivoted arm l9, which is pivoted intermediate its ends to a swinging arm on a pivotal pin Ha. Said swinging arm is transversely pivoted to a stationary support bracket 2| on a pivotal pin 20a. A coil spring 22 is interposed between the insulating board i6 and the free end of the arm i9 and is adapted to move the contact I! to an open position with a wiping action by pivoting said swinging arm 20 about the axis of the pin 20a against a fluid plunger 25. The swinging arm 20 is provided with an engaging abutment 23 projecting outwardly therefrom, which is engaged with an engaging member 23 on the end of the plunger 25. Said plunger is slidably mounted in a bearing 26, carried in an end wall of the casing l4, and extends outwardly from said casing into a fluid chamber 30, formed in a cylinder 3i secured to the outside of said casing. A fitting 32 connects said fluid chamber with a distributor valve 33 through a pipe 34. Suitable packing is provided to prevent fluid from entering said casing. Thus when fluid is admitted to the chamber 30, the plunger is moved in a direction to pivot the arm about the axis of the pin 20a to engage the contact IS with the contact El. Said plunger then pivots the arm [3 about the axis of the pin l3a-to fully engage said contacts against the spring 22 with a wiping action, it being understood that the spring 22 serves to disengage said contacts, when pressure is released from said chamber and to exhaust fluid from said chamber. The fluid operating mechanism for the contactor is entirely outside of the contactor casing, so that no fluid will enter said casing. -A leakage drain (not shown) may be provided to permit fluid which may leak past said plunger to return to the fluid storage tank.

Referring now in particular to the fluid diagram illustrated in Figure 1, a fluid pump 45 is provided to effect pressure in the system. Said pump is connected with an accumulator 35 by means of a pipe line 44, which accumulator serves as a fluid storage tank for the hydraulic system. Said accumulator may be of any well known form and, as herein shown, includes a cylindrical tank 36 having a cover 31. Said cover is provided with an inwardly extending cylindrical portion 33, ex tending within and opening into said tank. A cylindrical piston 39 is mounted on said cylindrical portion 38, for slidable movement with respect thereto. Said piston has a closed inner end and a flanged portion 40, adapted to abut the inside of said cover 31, when said piston is in a retracted position. A pair of concentrically arranged compression springs 4| and 42 are interposed between the bottom of said tank and the inside of said flange of said piston, to urge said piston into a retracted position.

A high pressure pipe line 43 connects the in wardly extending cylindrical portion 38 of said accumulator with the pump 45 through a relief valve 46, so that pressure in the fluid system will supply pressure to said cylinder 38 and cylindrical piston 39 and move said piston against the compression springs 4i and 42, to compress said springs. The strength of said springs is such that fluid under pressure accumulated in said cylinder and piston, will be supplied to the system through said springs, whenever said fluid pump stops.

The pump 45, which supplies fluid under pressure to said accumulator and to the hydraulic system, is herein shown as being a well known form of gear pump and is connected with the relief valve 46 by means of a pipe line 41. Said relief valve has connection with the pipe line 43, leading to the pressure side of the accumulator, by means of the pipe line 44, which is also connected to a pressure pipe line 50, leading to a control valve 5|, which serves to supply fluid to the distributor valve 33 at progressively increasing or decreasing pressures, through a control pipe line 52. A low pressure pipe line 53 leads from said relief valve to the cylindrical tank 35 of the accumulator 35.

The relief valve 46 is so arranged that under normal pressures fluid will pass from the pipe line 41 through a chamber 54 of said valve, through a passageway 55, and chamber 56, to and through a check valve 51 to the pipe line 44. Upon overload, fluid under pressure in the chamber 53 will move a piston 58 in said chamber 58 against a spring 59, to a position to open a port to a passageway 60, to permit fluid under pressure to engage the under side of a piston 6| in the chamber 54. This will move said piston against a spring 62 and open a port leading to a passageway 63, to bypass fluid through said passageway to the tank 36 of accumulator 35, through the pipe 53. Upon the release of pressure, the spring 59 will move the piston 58 in a direction to close the passageway to fluid under pressure and open said passageway to the return line 53. At this time pressure will be relieved from the piston BI, and the spring 32 will move said piston in a direction to close the passageway 63.

A pipe line 64 leads from the pipe line 50 to a 4- way valve 65, which serves as a reversing valve, for reversing the direction of the flow of fluid to a reversing cylinder 56. Said cylinder is provided to operate a reverse drum 59 for the motors of the locomotive and has a piston 61 movable therein, which is connected with said reverse drum by means of 9. depending in 10 (see Figures 3 and 4). Said reversing cylinder 65 is shown as being mounted on the outside of a casing 38 for said reverse drum and the contacts therefor. The pin I0 depends from said piston, intermediate the ends thereof, and extends through a slot H in the lower portion of said cylinder and has engagement at its lower end with a slotted lever arm 12, secured to the upper end of a shaft I3, upon which said reverse drum is mounted. Rectilinear movement of said piston in one direction or another will thus turn said reverse drum 63 to a forward or reverse position in an obvious manner.

The body of the reversing cylinder 66 is provided with a longitudinally extending pressure passageway 14 opening into said cylinder at longitudinally spaced points,' which are spaced equally from the transverse center of said cylinder so that one or the other openings to said passageway will be uncovered by said piston when said piston is in one extreme position or another. Said passageway is connected with a pressure pipe 15, which is connected with the distributor valve 33, for supplying fluid under pressure to the fluid-operating mechanism for the contactors I to 8 inclusive, in a manner which will hereinafter more clearly appear as this specification proceeds.

Since the passageway 14 is only open to the cylinder 65, when the piston 51 is in one extreme position or another and the reverse drum is in either a forward or reverse position, fluid under pressure can only flow from reversing cylinder 88 to the distributor valve 33, when said reverse drum is in one of these positions. Thus, a hydraulic interlock -is provided between said distributor valve and reverse drum, to prevent operation of said distributor valve, until said reverse drum is in the proper operating position.

Another passageway 18 is provided in the cyl' inder 88 to take care of any leakage between the piston 81 and the walls of said cylinder. A pipe 11 leads from said passageway to a pipe 18, which connects with the drain pipe 53, leading to the storage tank 38 of the accumulator 35.

The distributor valve 33 is provided with a cylindrical chamber 8|, having a piston 82 movable therein. Said piston has three spaced apart lands 83, 84 and 85, the land 83 being at the end of said piston adjacent the inlet from the control pipe 52, so that fluid under pressure, entering said valve from said pipe, will move said piston against a coil spring 88, interposed :between the inner end of said chamberand the end of said piston opposite from the land 83.

A drain passageway 88 is provided in the body of the distributor valve 33 and leads from a position between the lands 83 and 84 to a position above the land 85, when the piston 82 is in an extreme on position, to take care of any leakage of fluid past said lands 83, 84 and 85. Said drain passageway is connected with the pipe 18, which leads to the tank 36 of accumulator 35.

The pressure pipe 15 enters the distributor valve 33, intermediate the ends thereof at a point disposed adjacent the lower end oi the land 85, when the piston 82 is at an extreme on position and the spring 88 is extended, as in Figure 1. The lands 84 and 85 are so spaced that fluid under pressure will be supplied in the space between said lands by said pressure pipe, in all positions of said piston in said cylindrical chamber 8|. It should be noted that fluid admitted from the pipe 15 acts equally in opposite directions on the piston 82, so has no tendency to move said piston in the direction of its axis.

Pipes 90, 9|, 92, 93, 84 and 85 lead from ports in the chamber 8|, which are disposed on the opposite side of the land 85 from the lands 83 and 84, when the piston 82 is in an off position. Said pipes are so arranged that the respective passageways connecting said pipes to the chamber 8| will be successively uncovered by the land 85, to admit fluid under pressure from the pipe 15 thereto, upon movement of the piston 82 against the spring 88. Thus, as the piston 82 moves to successively uncover the passageways 98 to 95 inclusive, the contactors associated therewith will be closed in the hereinbefore described manner, to connect the motors of the locomotive in the main line circuit, and to cut out the resistance 43 from the motor circuit, step by step, under control o1 the operator.

The strength of the spring 86 is such that the piston 82 will move to uncover the passageway leading from the pipe 90 when fluid enters the chamber 8|. from the pipe 52 at a predetermined pressure, and will uncover the next passageway when the fluid pressure increases a predetermined amount, and so on until all of the passageways are uncovered step by step.

It will be understood that in order to insure proper functioning of the distributor valve 33 in the manner above described, the control valve 5| for supplying pressure to the chamber 8| must be such as to produce uniformly accurate and positive step-by-step pressure values in said chamber corresponding with the several positions of the control handle 19 of said control valve. Ordinary hydraulic control valves, as well as socalled hydraulically balanced valves, have been found inadequate for this purpose, due mainly to certain inherent characteristics of such valves which tend to produce difierent pressure .values at the same position of the control handle, de-

pending upon whether the said handle is being moved toward its on or its oi! position. For instance, valves of the sliding piston type can be hydraulically balanced but they necessarily operate with a time lag in opening or closing, which produces substantial variations in step-by-step pressure output, depending upon whether the pressure is to be reduced or increased. On the other hand, valves of the poppet type open and close almost instantaneously, but it is much more difllcult to balance valves of the poppet type so that they will always open or close at exactly the same predetermined pressures, because they are subject to uneven or variable distribution of pressure on their valve seat areas. Such variations are caused by changes in the eifective area of contact between the valve and its seat due to numerous unpredictable factors, such as infinitesimal inaccuracies in machining, wear, variations in operating pressures, temperature changes, or the like.

Referring now in particular to the control valve 5|, which supplies fluid under pressure to the distributor valve 33 through the control line 52, at uniformly increasing or decreasing pressures, which change step by step for each port opening of said distributor valve as a control handle 19 of said valve is turned by the operator in one direction or another, said control valve is especially designed to maintain substantially the same pressures in the control line at the same position of the control handle, when said control handle and valve are turned in an on or an off direction. Said control valve, as herein shown, is in the form of a triple valve including a block 96 having three valve elements 91, 98 and 99 therein, controlled in unison by the control handle 19.

The valve element 91 is of the piston type and serves as a charging valve for controlling the admission of fluid under pressure to the pressure side of the valve element 98. The variation in pressure resulting from said charging valve as it is admitting fluid from a lower to a higher pressure and from a higher to a lower pressure, is independent of pressure in the intake pressure line 50, and is due mainly to the lap of the piston which introduces a time lag in the opening and closing of said valve. As previously explained, a single valve of this type would not be sufiiciently accurate to insure full and accurate opening of the ports in the distributor valve.

Valve 98 is of the poppet type and includes separate pressure and release poppet valves, the normal characteristics of which are such that they will open practically instantaneouslyon the slightest movement of their control means. Said valves, however, are subject to the errors inherent in poppet valves due to the unbalanced pressures on proper pressures corresponding with diflerent positions of the control handle, with little or no error, when the valve elements 01, B and 80 are simultaneously turned in an on or an oflf direction.

The valve element 99 is of the piston type similar to the valve element 91, and fluid discharged through the valve element 98 is discharged through the end of said valve element 99. This valve element may therefore be called a discharge valve. This valve element and the valve element 91 serve to maintain predetermined pressure difierences on opposite sides of the poppet valve element 98, which will be within a; certain tolerance throughout the entire pressure range thereof, thereby reducing any pressure inaccuracies that might be caused by unbalanced pressures on the valve seat areas of said poppet valves, as will hereinafter more clearly appear as this specification proceeds. These three valve elements are thus combined and controlled in unison so the pressure errors of one valve will be corrected by the other, to accurately maintain the pressure in the control line to very close limits in order that there may be no chance of a port of said distributor valve being partly open at a position of the control handle when it should be fully open.

The valve elements 91, 90 and 99 communicate with three aligned cylindrical chambers I00, MI and I02 formed in the block 90 of the valve element 5| (see. Figures '1, 9 and Said chambers are each connected with the low pressure side of the accumulator 35 by means of passageways I 03, I03, connecting the outer chambers with the inner chamber (see Figure 7), and a passageway I04, connecting the inner chamber with the return pipe 53 (see Figure 10). Said chambers I00, IM and I02, besides forming return passageways for the fluid, also form enclosures for the control means for said respective valve elements 91, 08 and 99.

Operation of the valve elements 91, 00 and 00 is controlled simultaneously by means of a gear I05, on a shaft 89, upon which the control handle 19 is mounted (see Figures 5 and 6). The teeth of said gear have elongated faces and mesh with teeth formed in cylindrical valve operating sleeves I01, I08 and I09, which are slidably mounted within the chambers I00, IM and I02 respectively. Said valve operating sleeves are each mounted on a flanged portion of a hollow supporting member I I I, which is closed at its inner end and which extends within each sleeve. Each of said supto cause an even pressure to be exerted on said valve by said spring.

A compression spring H1, in the chamber IOI, extends within the valve operating sleeve I00 of valve element 90 and is seated at one of its ends in said sleeve. The opposite end of said spring is seated in a seat H0, freely connected with the inner or right-hand end of a slidable hollow piston H0 0! the valve element 00, through a pin I20 (see Figure 9).

In a like manner, the valve operating sleeve I08 of valve element 00 has a compression spring I22 seated therein at one 0! its ends, and seated within a seat I20 at its opposite end. Said seat is freely mounted on the inner or right-hand end of a piston valve I24 of the valve element 09.

Fluid under pressure from the accumulator enters the charging valve element 01 through a passageway I20, connected with the pipe 00. This passageway is connected with said valve element by a port I21 in a valve cylinder I20, for said valve element. Said passageway is connected with the discharge valve element 09 by a port I14 in a valve cylinder I01 of said valve element. A passageway I44 connects said valve element 01 I with the pressure adjusting valve element 00, and

porting members is slidably mounted on a pilot I I2, which is bored to admit fluid therethrough to the inside of its associated supporting member, to exert a pressure on said supporting member in a direction to move said member along said pilot. Each of said pilots is herein shown as being secured to and extending inwardly from a threaded plug I I3, which plugs are threaded in the outer or right-hand ends of said chambers.

A compression spring II4 extends within the valve operating member I01 of valve element 91 and is seated at one of its ends in the flanged portion of the member III. The opposite end of said spring abuts a washer I15 on a seat H0, freely mounted on the inner or right-hand end of a piston valve H6 for the valve element 91. Said washer is provided to give a predetermined pressure difference between the valve elements 91 and 98, as will hereinafter more clearly appear as this specification proceeds. The connection between said seat and piston valve is loose, to avoid binding between said seat and valve and a passageway I00 connects said pressure adjusting valve element 08 with valve element 00.

The piston valve I I0 of the chargin valve ele-- ment 91 has a land or piston I29 at the left-hand end thereof, which laps the port I21 and which serves to control opening or closing thereof (see Figures 7 and 8). Another land or piston I00 is spaced longitudinally from said land I20 and serves to guide said piston valve for movement along said cylinder. A third land or piston I II is spaced from said last mentioned land, adjacent.

the right-hand end of said piston valve. Said last mentioned land serves as a valve to open or close the discharge opening from said cylinder to the chamber I00. Said piston valve is drilled longitudinally from the left-hand end thereof, for a portion of its length. Cross passages I02 are drilled to the right of land I29 and communicate with said longitudinal bore, so fluid under pressure may pass through said longitudinal bore and exert pressure on the left-hand end of said piston, to balance the pressure of the spring II4. Cross passages I24 are also bored between the lands I00 and IOI, so fluid may pass through said longitudinal bore out through said cross passages into the chamber I00, when said piston valve is moved to the right and the land IOI is out of lapping engagement with the valve cylinder I28. The lands I20 and I3I are so spaced with relation to the port I21 and the end of the valve cylinder I20, that both ports may be closed at the same time with some lap at each valve.

A port I40 is provided in the valve cylinder I20, to the right of the port I21. Said port I40 communicates with the passageway I44, and with a passageway I, which leads to the passageway in the pilot II2, for the valve operating sleeve I01. Pressure may thus be applied to the inside of the closed end of the hollow supporting member III, to exert a force on said supporting member and valve operating sleeve in a direction towards the left, so as to balance the pressure of the spring II4 against said valve operating sleeve and the control handle 10.

When the valve piston II I is moved to a position where fluid under pressure will pass through the port I21 into the annular space between the reduced portion oi said valve piston and the inside or said cylinder walls, fluid will flow through assasas the port I46 to the hollow supporting member for the valve operating sleeve I61. It will also flow through the passageway I44 to the pressure ad- Justing valve element 66.

The piston valve I24 of the discharge valve element 99 is slidably mounted in a valve cylinder I61. Said piston valve is provided with three spaced lands or pistons I69, I10 and III, similar to the lands I29, I60 and III of the piston valve III. A longitudinal passageway is drilled from the left-hand end of said piston valve. passageways I12 are drilled into said central passageway between the landsvl69 and I10. Cross passageways I13 are drilled into said central passageway between the lands I10 and I1 I, to release fluid through the inner end of the valve cylinder I61. Fluid entering said longitudinal passage through the cross passageways I12 may'also exert pressure on the left-hand end of said piston, to balance the pressure oi the spring I22. The lands I69 and III are so spaced with relation to the port I14 and end of the cylinder, that both ports may be closed at the same time, with some lap at each valve.

When the valve I69 01 the valve element 99 is open, fluid will flow throughthe sleeve I61 in the space between the lands of the piston valve I24, through the passageway I60 and a passageway I16, to and through the pilot II2 of the valve operating member I06, to balance the pressure of the spring I22 on the control handle 19. Fluid will also flow through the central passageway in said piston to the head end of said piston valve, to exert pressure thereon and balance the pressure the spring I22 exerts against said piston valve.

The pressure adjusting valve element 96 consists of a poppet valve II which controls the admission of fluid to the control line I52 and a poppet valve I56 which controls the release of fluid from said control line, as will hereinafter more clearly appear as this specification proceeds. Said pressure adjusting valve includes a hollow threaded head I45, threaded in the left-hand end of the valve block 96, the hollow portion of which head has a reduced left-hand end of a. plunger I41 slid-ably mounted therein. A coil spring I46 in said threaded head abuts the left-hand end Cross of said plunger and tends to move said plunger to the right. A fixed valve cylinder I49 is spaced to the right of said threaded head and the space between said threaded head and cylinder forms a passageway for fluid from the valve element 91. The left-hand end of said valve cylinder is shaped to form a seat, which is adapted to be engaged by the right-hand end of an enlarged portion I50 of said plunger I41. Said enlarged portion and seat thus form the poppet valve I5I sea'ted against the end of the valve cylinder I49, which will open or close upon a very slight movement of said plunger. Said poppet valve is adapted to open or close a passageway through said cylinder I49, leading to passageways I53 in said cylinder, which communicate with a pressure passageway I26 and the control line 52, for supplying fluid under pressure to the distributor valve 33. A passageway I54 leads from passageway I26, to and through the pilot for the valve operating sleeve I08 and to the hollow member III for said valve operating sleeve, for balancing the spring pressure exerted against said valve operating sleeve and the control handle 19.

The right-hand portion of the valve cylinder I49 has the hollow piston H9 slidably mounted therein. Said hollow piston has the right-hand end of the plunger I41 slidably mounted therein. The left-hand end of said hollow piston is shaped to form a seat for the right-hand end of an enlarged valve portion I66 0! said plunger I41, to form the P ppet valve I 66, which controls the flow oi fluid through the passageway I60 to the discharged valve element 99.

Displacement oi the spring II4 towards the valve cylinder I49 will move the hollow piston I I9 and plunger I41 in a direction to open the poppet valve I6I, to admit fluid under pressure to the pressure line I66. Fluid pressure exerted on said hollow piston to the right, against said compression spring II1, will tend to'move said hollow piston to the right to open the valve I56 and permit the discharge 0! fluid through the passageway I60. The plunger I41 is longitudinally drilled from the left-hand end thereof and is cross-drilled just to the right oi the valve I5I, to admit fluid under pressure to the left-hand end of said plunger. Pressure is exerted on the right-hand end of said plunger through a passageway I52, a port I66 in the valve cylinder, and a passageway I66 in the hollow piston II9. Pressures will thus be exerted on the left-hand end of said plunger to balance pressure'exerted against the righthand end of said plunger, and will also be exerted in a direction towards the left in the annular spaces under the valves I6I and I56. This gives an accurate balance for the valves except for the pressure that is on the valve seats. Pressure is also exerted on the hollow piston H9 in a direction towards the right, against the spring II1, to balance said spring and tend to open the poppet valve I56. The poppet valve I5I is closed by the spring I46 and by pressure on the head end of the plunger I41.

Since the distribution of pressure on the poppet valve seat I5I may be irregularly distributed, it cannot be accurately determined and it cannot be counterbalanced. Thus, if pressure is applied from the valve spring through the piston H9 and valve I56 to open valve I5I, it must overcome any pressure that is exerted against the valve seat of the valve I5I. I If pressure were admitted to this valve directly from the accumulator through. passage I44, and it was desired to established a comparatively low pressure in the control line 52, suflicient extra pressure would have to be put on the spring I I1, to overcome the unbalanced pres sure on the valve seat. This would result in com siderable inaccuracy. The reason is that after the valve has once opened, the unbalanced pressure will be changed and it will not close at a point corresponding to the handle position at which the valve opened. If, however, the pressure differences between the passage I44, through which fluid is admitted to the valve, and the passage I66 from which fluid is discharged, are kept small; that is, not greater than twice an assumed pressure which will be designated as A pounds per square inch, the unbalanced pressure on the valve seat becomes extremely small and the pressure in con trol line 52 can be held to a small tolerance. The valve seat of valve I56 also has an unbalanced pressure and the same situation exists there. It is therefore the duty of valve element 89 to maintain a pressure in passage I60 between zero and A" pounds per square inch below the desired pressure in the control line 52, and it is the duty of valve element 91 to maintain a pressure in passage I44 between zero and A pounds per square inch above the desired pressure in the control line 62,

The theory of operation of the pressure control valve mechanism will now be described.

When the operating handle ll is at an oi! position, the spring Ill oi the charging valve element '1 should exert a pressure which will balance a predetermined pressure in the passageway I, which for the purposes or illustration may be designated as A pounds per square inch, when the right-hand edge oi the piston or land I2! is in line with the right-hand edge of the port I21, and all of the lap is on the piston or land I3I, closing the cross passages I to the return. There will thus always be a pressure of A" pounds per square inch in the passageway I, when the valve is in an oil position.

The spring I22 of the discharge valve element 9!, bearing against the end of the piston valve I24, should be free, and the right-hand edge or the land I6! should be in line with the righthand edge 01' the port I'll and all 01' the lap should be on the land I".

Both poppet valves ISI and IN should be closed and the spring I" in valve element 98 should be compressed to an amount that will balance "A" pounds per square inch on the righthand end of the hollow piston III.

In the form shown herein, the valve elements 81 and 99 are alike in all respects, so the increased pressure on valve element 91 is accomplished by placing the washer I'l5 under the spring I, said washer herein being shown as having a thickness approximately equal to the lap of the land I3I of said valve element 91 when the operating handle 18 is at an oil! position. Said lap is equal to the combined laps of the valves I29 and I3I when the port I2l is just closed and the valve I3I is fully lapped.

When the control handle is in this oil position, and the right-hand edge of the piston I29 is in line with the right-hand edge oi the port I21, any leakage of fluid through the valve formed by said land will permit fluid to flow in the annular space between the reduced portion of said valve piston and the inside of said valve cylinder, to the passage I and to the pressure adjusting valve element 98. It will also flow through the hollow valve center to the head or left-hand end of the piston valve IIB. As pressure builds up against the head of said piston valve, it will force said piston valve against the spring H4 until the leakage is stopped, or until the land l3l opens the end of the valve cylinder.

Also, any leakage through the valve formed by the land ififi'of the discharge valve element 99 will permit fluid to flow into the annular space between the valve cylinder I57 and the reduced portion of the piston valve I24, into the passage 560. It will also how through the hollow valve center to the head end of said piston valve. As pressure builds up against the head end of said piston valve, will force said piston valve against .the spring 322 until the leakage is stopped, or

untilthe piston iii opens the end of the valve cylinder. This will cause a release of pressure in the annular space between the valve cylinder and reduced portion oi the valve piston, until the valve is loaian'ced, which will prevent the further discharge of fluid.

If the increases in pressure in valve elements 91 and 99, ca by opening the valves I29 and I69 against their respective springs, is designated as A pounds per square inch as before, then for any position of the operating handle, the pressure in passage I may increase from the aseacos pressure in the control line '2 by the amount of "A pounds per square inch, and the pressure in passage I" may vary from the pressure in the control line by the amount of "A" pounds per square inch lower than the pressure in said control line, according to whether the position has been reached from one of higher pressure or from one or lower pressure, and according to the relative leakages oi the valves I2! and lil and the valves I" and I'll.

If the control handle II is moved from a lower pressure position to a higher pressure position,

the spring I of the charging valve element 01 will force the piston I28 to open the port I21, admitting iiuid from the accumulator ll through port I21 and through the hollow valve stem to the head of the valve piston II. This admission of fluid will normally cease when the port closes, and the pressure built up in passage I will depend upon the eflort exerted by the spring in this position, but it the valve I2! continues to leak, additional pressure will be built up, forcing the piston valve against the spring until possibly the valve I3I is open, in which case the pressure in the passageway I would have been increased by an amount equal to "A" pounds per square inch.

The spring I22 of the discharge valve element 98 will also force the land or piston I" to open the port I14, admitting fluid from the passage l2! and through the hollow valve stem to the head end of hollow valve piston I24. When the port closes, the pressure built up in the passage I60 will depend upon the effort exerted by the spring I22, but if the valve It! continues to leak, additional pressure will be built up until possibly the land III is open, in which case the pressure in the passageway I" would have been increased by an amount qual to "A" pounds per square inch, as in the valve element 91.

If it is assumed that a pressure of pounds per square inch is desired in the control line 52 and that the pressure difference A is equal to 30 pounds per square inch when the control handle is in an off position, when the control handle is turned to a position corresponding to 100 pounds, fluid from the accumulator 35 will be admitted to valve element 81 until 100 pounds pressure has been built up against the piston valve H8, at which point this valve will close. The 100 pounds pressure built up in valve'element 91 will be applied to valve element 98 through passage I. Pressure from the accumulator will be admitted to valve element 89 until a pressure of '70 pounds has been admitted to said valve element and through it and passage I60 to valve element 98 The poppet valve I5I will be open at the same time the valves in valve elements 9'! and 99 open, and the pressure from valve element 91 through passage i into the valve cylinder I49 and passage I25 will be applied to the control line 52. When this 100 pounds pressure has been reached in the control line, valve I5I will return to its seat and the distributor valve will respond to the 100 pounds pressure. Since the pressure admitted through the poppet valve I5I from the passageway H4 exceeds the back pressure effective on the poppet valve I56 from the passageway I60, the latter poppet valve I56 remains closed.

If while the operating handle is in a position to give 100 pounds pressure to the distributor valve, fluid may leak through valve element 81 into passage i until I30 pounds pressure has been reached, any leakage that would tend to carry the pressure beyond this point will be reseat.

leased through the valve I8I at the end of the cylinder. i

It the control handle is now advanced to a point calling for 200 pounds in the controlpipe 82, valve elements 91 and 99 will open, to admit fluid to passages I44 and I88, the same way as before. At the same time, the valve element 98 by responding more quickly than either valve elements 91 or 99, will be open against a back pressure of not over 30 pounds per square inch distributed over the valve seat. When 200 pounds pressure in the control line has been reached, all of the valves are closed.

While the pressures applied to passage I44 might exceed those in control pipe 52 by 30 pounds, and the pressure in passage I80 will be not over 30 pounds less than the pressure in control pipe 52, the pressure in said control line will vary only a few pounds from the desired pressure because it requires only a few pounds difference in pressure, to overcome the unbalanced valve seat areas against a back pressure of 30 pounds per square inch over the relatively small area of the valve seat of the valve II.

When the control handle 19 is moved in an off direction from a point calling for 200 pounds pressure in the control line 52 to a point calling for 100 pounds in said control line, the foregoing operations will be reversed. Fluid will be released from the control line 52 through the poppet valve I58, passage I80 and valve Ill, and will be released from the valve element 91 through the valve I3I and end of the valve cylinder to the spring chamber I02. The pressure difference on opposite sides of the valve I58 will be maintained by the valves III and I3I .to overcome the unbalanced pressure on the valve The reductions in pressures exerted by the spring H4 and I22 of the respective valve elements 91 and 99 will allow pressure on the head ends of the valve pistons H8 and I24 to open the passageways from the ends of valve cylinders I28 and I51 to the respective chambers I00 and I02 and the return line 53. Pressure will be released from the valve cylinder I51 until a pressure of 100 pounds is reached in the passageways I54 and I88. Pressure will also be released from the chamber I28 until a pressure of 130 pounds is reached in the passageway I44.

At the same time the valve element 99 opens to the return, the poppet valve I58 will open against a back pressure and not over 60 pounds per square inch on the valve seat and will close when a pressure of substantially 100 pounds is reached inthe control line.

A notching cam 81 on shaft 89 for the control handle 19 is provided with a plurality of spaced notches I18; I18 formed in the periphery thereof, which designate the various positions at which definite step by step pressures are established and maintained in the control line 52, so that the distributor valve 33 will have a full opening of the corresponding port. The various positions of said control handle are indexed by means of a roller I19 on the end of a rocking arm I80, which is yieldably pressed into engagement with said notches I18 by means of a spring I8I, engaging said rocking arm.

An interlocking connection is provided between the control valve SI and the 4-way reversing valve 85, to prevent operation of said reversing valve except when said control valve is in an off position, and to prevent operation of said control valve except when said reverse valve is in a forward or areverse position. Said interlocking connection, as herein shown, in-

'cludes a disk m. secured to, the shaft as, just above the notching cam 81, and adapted to be engaged by an engaging end I84 of a rocking arm I85. Said disk is provided with a notch I88 on the face thereof, which corresponds with the of! position of said control valve, and which is adapted to be engaged by said projecting engaging end. Said rocking arm is provided with an engaging end I89, spaced from and extending in an opposite direction from the engaging end I84, which is adapted to register for engagement with either one of a pair of notches I90, I90 on alocking plate I9I, which is secured to a shaft I92 for said reverse valve 65.

When the control valve 5I is in an off position, the projecting end I84'of the rocking arm I may engage the notches I88, I86 of the disk I83. When said end of said rocking arm is in engagement with said recessed portion of said disk, the locking plate I9I and valve shaft I92 will be free to pivot. When the reversing valveis in an intermediate position, between an extreme forward or reverse position, the engaging end I89 of the arm I85 will engage the high spot between the notches I90, I98 and the engaging end I84 will be held in engagement with the recessed portion I88, to lock the control handle 19 against turning until the locking plate I9I is in a position to permit the engaging end I89 to drop into either one of the notches I90, I98, at which time said reverse drum will be in either a forward or reverse position. When said engaging end I84 is moved out of engagement of said notch I88, said engaging end I89, engaging either of said notches I90, I90, will be held in engagement with either of said notches by said engaging end I89 and star wheel, to lock said reversing valve from turning movement until said control handle 19 has been moved to turn the control valve 5| to an extreme oif position, so said engaging end I84 may drop into the notch I88.

While I have herein shown and described one form in which my invention may be embodied, it will be understood that the construction thereof and the arrangement of the various parts may be altered without departing from the spirit and scope thereof. Furthermore, I do not wish to be construed as limiting my invention. to the specific embodiment illustrated, excepting as it may be limited in theappended claims.

I claim as my invention:

1. In a. variable pressure hydraulic control valve, a valve block, a pressure inlet leading into said block, a variable pressure passageway in said block, a low pressure discharge outlet, at chamber in said block, a valve in said chamber controlling the passage of fluid from said pressure inlet to said pressure outlet, said valve including a pair of cooperating poppet valves for controlling the passage of fluid from said inlet to said outlet and from said outlet to said discharge opening, and comprising a sleeve having passageways therein leading from said inlet to said outlet, a hollow piston slidably movable within said sleeve and having passageways therein communicating with said pressure inlet and discharge opening, a plunger slidably movable within said sleeve and hollow piston, said plunger having a pair of valves thereon, one of said valves being adapted to be seated against one of said sleeves and form one poppetvalve, for opening or closing the passageway therein and the other of said valves being adapted to be seated against said other sleeve and form the other poppet valve,

for opening or closing the passageway therein, a spring in said chamber and having engagement with said hollow piston for urging said piston in a direction to close said discharge poppet valve and open said pressure poppet valve, and means for displacing said spring to increase or decrease the pressure of fluid in said pressure outlet.

2. In a variable pressure hydraulic control valve, a valve block, a pressure inlet leading into said block, a variable pressure passageway in said block, a low pressure discharge outlet, a chamber in said block, a valve in said chamber controlling the passage of fluid from said pressure inlet to said pressure outlet, said valve including a pair of cooperating poppet valves for controlling the passage of fluid from said inlet to said outlet and from said outlet to said discharge opening, and comprising a sleeve having passageways therein leading from said inlet to said outlet, a hollow piston slidably movable within said sleeve and having passageways therein communicating with said pressure inlet and discharge opening, a plunger slidably movable within said sleeve and hollow piston, said plunger having a pair of valves thereon, one of said valves being adapted to be seated against one of said sleeves and form one poppet valve for opening or closing the passageway therein and the other of said valves being adapted to be seated against said other sleeve and form the other poppet valve, for opening or closing the passageway therein, a spring in said chamber having engagement with said hollow piston for urging said piston in a direction to close said discharge poppet valve and open said pressure poppet valve, means for displacing said spring to increase or decrease the pressure of fluid in said pressure outlet, fluid means acting against said hollow piston and spring for balancing the pressure of said spring and causing said piston to move against said spring to close said pressure poppet valve and open said discharge poppet valve, and a pair of piston valves connected with said pressure inlet, for reducing the pressure therein and maintaining a pressure diflerence on opposite sides of said poppet valves within predetermined limits, throughout their entire pressure ranges.

3. In a variable pressure hydraulic control valve mechanism, a high pressure line, a variable pressure lin control handle for operating said valve, means operated by said control handle for causing said valve to establish the same pressures in said variable pressure line for the same positions of said control handle when said control handle is moved in an on or an off direction, including two piston valves, connections from said high pressure line to the inlet sides of said piston valves, two poppet valves, the pressure discharge side of one piston valve being connected with the inlet side of one poppet valve and the discharge side of the other poppet valve being connected with the pressure discharge side of the other piston valve, said valves being simultaneously operable and said piston valves being arranged to maintain pressure differences on opposite sides of said poppet valves within predetermined limits, to reduce the variations in opening and closing pressures of said poppet valves caused by the unbalanced pressures on the valve seats thereof.

4. In a variable pressure hydraulic control valve mechanism, two piston valves, a high pressure line, a connection from said high pressure line to each of said piston valves, two poppetvalves, a variable pressure line connected with said popp t valves, one of said valves being arranged to supply fluid under pressure to said variable pressure line and the other of said poppet valves being arranged to release fluid from said variable pressure line, a return line leading from said last mentioned poppet valve to one of said piston valves, means for operating said valves in unison, a. pressure connection from one piston valve to said poppet valve which supplies fluid under pressure to said variable pressure line, and a pressure connection from said other piston valve to said return line, for maintaining a pressure difference between said pressure connection to said poppet valve which supplies fluid under pressure to said variable pressure line and said return line within predetermined limits throughout the entire pressure range of said control valve.

5. In a variable pressure hydraulic control valve mechanism, a variable pressure line, two pressure controlled poppet valves, one of which serves to admit fluid to said variable pressure line at a predetermined pressure and the other of which serves to release fluid from said pressure line, a high pressure line, two piston valves connected with said high pressure line, means for operating said piston and poppet valves in unison, one of said piston valves being adapted to supply pressure from said high pressure line to said poppet valve which controls the admission of pressure to said variable pressure line, at a pressure reduced from the pressure of said high pressure line, and the other of said piston valves being adapted to control the admission of pressure to the discharge side of said poppet valve which controls the release of pressure from said variable pressure line at a pressure reduced from the pressure in said high pressure line, and also being adapted to release fluid pressure from said last mentioned valve, to maintain a pressure diiference on opposite sides of said poppet valves within predetermined limits throughout the entire pressure range of said control valve to reduce the variation in opening and closing pressures of said poppet valves caused by the unbalanced pressures on the valve seats thereof.

6. In a variable pressure hydraulic control valve mechanism, a high pressure line leading to said valve, a variable pressure lin leading from said valve, a poppet valve for controlling the admission of fluid under pressure to said variable pressure line, another poppet valve for releasing fluid from said variabl pressure line, and means operable simultaneously with said poppet valves for reducing the unbalanced pressure on the valve seats of said poppet valves to a minimum value and for maintaining this unbalanced pressure at a minimum value throughout the entire ressure range of said valves including a piston valve adapted to admit fluid at a. pressure reduced from the pressure in said high pressure line to the pressure side of said first mentioned poppet valve, another piston valve adapted to admit fluid at a pressure reduced from the pressure in said high pressure line to the discharge sid of said second mentioned poppet valve, which last named pressure may be of a lower value than the pressure in said variable pressure line, so said piston valves may maintain pressure difierences within predetermined limits on opposite sides of said poppet valves throughout their entire pressure range, to reduce the variations in opening and closing ressures of said poppet valves caused by the unbalanced pressures on the valve seats thereof.

assassa "I. In a variable pressure hydraulic control valve mechanism, a control handle therefor, a

highpressurelineleadingtosaidvalvaavariaL ble pressure line leading from said valve, and means for establishing the same pressures in said variable presure line for the same positions of said control handle when said control handle is moved in an on or direction including a for maintaining this unbalanced pressure at a minimum value throughout the entire pressure range of said valves including a variable pressure piston valve adapted to admit fluid at a pressure reduced from the pressure in said high pressure line to the pressure side of said flrst mentioned poppet valve, another variable pressure piston valve adapted to admit fluid at a pressure reduced from the pressure in said high pressure line to the discharge side of said second mentioned poppet valve, which last named pressure may be of a lower value than the pressure in said variable pressure line, so said piston valves may maintain pressure diflerences'within predetermined limits on opposite sides of said poppet valves throughout their entire pressur range, and means operated by said control handle for simultaneously operating said piston and poppet valves to cause apredetermined step by step increase or decrease in the pressure in said variable pressure line.

8. In a variable pressure hydraulic control valve mechanism, a control handl therefor, a high pressure line leading to said valve, a variable pressure line leading from said valve, and means for establishing the same pressures in said variable pressure line for the same positions of said control handle when said control handle is moved in an on or oil direction including a poppet valve for controlling the admission of fluid under pressure to said variable pressure line,

another poppet valve for releasing fluid from said variable pressure line, and means for reducing the unbalanced pressure on the valve seats of said poppet valves to a minimum value and for maintaining this unbalanced pressure at a minimum value throughout the entire pressure range of said valves including a variable pressure piston valve adapted to admit fluid at a pressure reduced from the pressure in said high pressure line to the pressure side oi. said flrst mentioned poppet valve, another variable pressure piston valve adapted to admit fluid at a pressure reduced from the pressure in said high pressure line to the discharge side of said second mentioned po pet valve, which last named pressure may be 01 a lower value than the pressure in said variable pressure line, so said piston valves may maintain pressure differences within predetermined limits on opposite sides of said popp t valves throughout their entire pressure range, and means operated by said control handle for simultaneously operating said piston and poppet valves to cause a predetermined step by step increase or decrease in the pressure in saidvariable pressure line, including a separate spring operatively connected with each of said piston valves, a third spring operatively connected with said poppet valves, and operative connections from said control handle to said springs for simultaneously displacing said springs.

9. In a variable pressure ulic control valve mechanism, a control handle therefor, a high pressure line leading to said valve, a variable pressure line leading from said valve, and valve means operable in unison i'or reducing the pressure from said high pressure line-and establishing the same pressures in said variable pressure line for the same positions of said control handle when said control handle is moved in an on or an oil direction including a substantially balanced poppet valve,coritrolling the admission of fluid under pressure to said variable pressure line, another substantially balanced poppet valve cooperating with said first mentioned poppet valve for releasing fluid from said variable pressure line, and means for reducing the unbalanced pressures on the valve seats oi said poppet valves and for maintaining these unbalanced pressures at such reduced values throughout the entire pressure ranges of said valves including a balanced piston valve adapted to reduce the pressure from said high pressure line and admit fluid at a reduced pressure to the pressure side of said flrst mentioned poppet valve, and another balanced piston valve adapted to reduce the pressure from said high pressure line and admit fluid at a reduced pressure to the discharge side oisaid second mentioned poppet valve.

10. In avariable pressure hydraulic control valve mechanism, a control handle therefor, a high ressure line leading to said valve, a variable pressure line leading from said valve, and means for reducing the pressure from said high pressure line and establishing the same pressures in said variable pressure line for the same positions of said control handle when said control handle is moved in an on or off direction including a substantially balanced poppet valve controlling the admission of fluid under pressure to said varialble pressure line, another substantially balanced poppet valve cooperating with said flrst mentioned poppet valve for releasing fluid from said variable pressure line, means for reducing the unbalanced pressures on the valve seats of said poppet valves and for maintaining these unbalanced pressures at such reduced values throughout the entire pressure range 01' said valves including a balanced piston valve adapted to reduce the pressure from said high pressure line and admit fluid at a reduced pressure to the pressure side of said first mentioned poppet valve, another balanced piston valve adapted to reduce the pressure from said high pressure line and admit fluid at a reduced pressure to the discharge side of said second mentioned p pp t valve, and means operated by said control handle for simultaneously operating said piston and poppet valves to cause a predetermined step by step increase .two cooperating poppet valves, a single spring for opening one of said poppet valves and closing the other of said poppet valves, means for balancing said poppet valves against said spring,

, means for simultaneously displacing said springs for operating said valves, the pressure discharge side or one piston valve being connected with the inlet side 01' one poppet valve, and the pressure discharge side of the other piston valve being connected with the outlet side of said other P ppet valve, so said piston valves will maintain a pressure diii'erence on opposite sides said poppet valves within predetermined limits throughout the entire pressure ranges of said valves, to reduce the variations in opening and closing pressures of said poppet valves caused by the unbalanced pressures on the valve seats thereof.

12. In a variable pressure hydraulic control valve mechanism, two piston valves, a separate spring for operating each or said valves, means for balancing said valves against said springs, two cooperating poppet valves, a single spring for opening one of said poppet valves and closing the other of said poppet valves, means for balancing said poppet valves against said spring, the pressure discharge side of one piston valve being connected with the inlet side 01 one poppet valve, and the pressure discharge side of the other piston valve being connected with the outlet side of said other poppet valve, so said piston valves will maintain a pressure difference on opposite sides of said poppet valves within predetermined limits throughout the entire pressure ranges of said valves, to reduce the variations in opening and closing pressures of said poppet valves caused .by the unbalanced pressures on the valve seats thereof, a control handle, and operative connections between said control handle and said springs, for simultaneously displacing said springs and operating said valves in unison.

13. In a variable pressure hydraulic control valve mechanism, a high pressure line, a variable pressure line, a control handle for operating said valve mechanism, and a plurality 01' valve means operated in unison by said control handle for causing said valve mechanism to establish the same pressures in said variable pressure line for the same positions of said control handle when said control handle is moved in an on or an oil! direction, including two piston valves, connections from said high pressure line to the inlet sides of said piston valves, a separate spring for opening each of said valves to admit pressure from said high pressure line, fluid passage means for balancing said valves against said springs, two poppet valves, 9, single spring for opening one of said poppet valves and closing the other of said poppet valves, fluid passage means for sub stantially balancing said valves against said spring, one of said poppet valves being connected with said variable pressure line, to supply fluid assasae under pressure thereto, and the other of said poppet valves being adapted to release fluid irom said variable pressure line, a connection irom the pressure discharge side 01- one piston valve to the pressure inlet side or said p pp t valve which supplies fluid under pressure to said variable pressure line, and a connection from the pressure discharge side of said other piston valve to the discharge side of said poppet valve which releases fluid from said variable pressure line, for maintaining a pressure diiierence on opposite sides of said poppet valves within predetermined limits throughout the entire pressure range of said valve, to reduce the variations in opening and closing pressures of said poppet valves caused by the unbalanced pressures on the valve seats thereof.

14. In a variable pressure hydraulic control valve mechanism, a high pressure line, a variable pressure line, a control handle for operating said valve mechanism, and means operated by said control handle for causing said valve mechanism to establish the same pressures in said variable pressure line for the same positions of said control handle when said control handle is moved in an on or an oil direction, including two piston valves, connections from said high pressure line to the inlet sides of said piston valves, a separate spring for opening each of said valves to admit pressure irom said high pressure line, fluid passage means for balancing said valves against said springs, two p pp t valves, a single spring for opening one of said poppet valves and closing the other of said poppet valves, fluid passage means for substantially balancing said valves against said spring, one of said poppet valves being connected with said variable pressure line, to supply fluid under pressure thereto, and the other of said poppet valves being adapted to release fluid from said variable pressure line, a connection from the pressure discharge side 0! one piston valve to the pressure inlet side of said poppet valve which supplies fluid under pressure to said variable pressure line, a connection from the pressure discharge side of said other piston valve to the discharge side of said poppet valve which releases fluid from said variable pressure line, for maintaining a pressure difference on opposite sides of said poppet valves within predetermined limits throughout the entire pressure range of said valve, to reduce the variations in opening and closing pressures of .said poppet valves caused by the unbalanced pressures on the valve seats thereof, and operative connections between said control handle and said springs for simultaneously displacing said springs and operating said valves in unison.

WILLIAM W. SLOANE. 

